The present invention relates to the manufacture of intraocular lenses (IOLs) for implantation in an eye. The present invention more particularly relates to a method for polishing selected areas of an IOL while other areas of the IOL remain unpolished.
A common and desirable method of treating a cataract eye is to remove the clouded, natural lens and replace it with an artificial IOL in a surgical procedure known as cataract extraction. In the extracapsular extraction method, the natural lens is removed from the capsular bag while leaving the posterior part of the capsular bag (and preferably at least part of the anterior part of the capsular bag) in place within the eye. In this instance, the capsular bag remains anchored to the eye's ciliary body through the zonular fibers. In an alternate procedure known as intracapsular extraction, both the lens and capsular bag are removed in their entirety by severing the zonular fibers and replaced with an IOL which must be anchored within the eye absent the capsular bag. The intracapsular extraction method is considered less attractive as compared to the extracapsular extraction method since in the extracapsular method, the capsular bag remains attached to the eye's ciliary body and thus provides a natural centering and locating means for the IOL within the eye. The capsular bag also continues its function of providing a natural barrier between the aqueous humor at the front of the eye and the vitreous humor at the rear of the eye.
One known problem with extracapsular cataract extraction is posterior capsule opacification, or secondary cataract, where proliferation and migration of lens epithelial cells occur along the posterior capsule behind the IOL posterior surface which creates an opacification of the capsule along the optical axis. This requires subsequent surgery, such as an Er:YAG laser capsulotomy, to open the posterior capsule and thereby clear the optical axis. Undesirable complications may follow the capsulotomy. For example, since the posterior capsule provides a natural barrier between the back of the eye vitreous humor and front of the eye aqueous humor, removal of the posterior capsule allows the vitreous humor to migrate into the aqueous humor which can result in serious, sight-threatening complications. It is therefore highly desirable to prevent posterior capsule opacification in the first place and thereby obviate the need for a subsequent posterior capsulotomy.
IOLs are typically either molded or lathe cut. Subsequent to either of these operations, the IOLs usually have flash, irregular, and/or roughened surfaces that need to be smoothed. It is thus usually necessary to polish the IOL to remove any flash and smooth out any rough areas on the IOL. A common IOL polishing method is tumble polishing wherein a batch of IOLs are placed in a tumbler for many hours with a polishing agent. Examples of tumble polishing IOLs may be seen in the following patents:
U.S. Pat. No. 5,133,159 discloses a method of tumble polishing silicone articles in a receptacle charged with a mixture of non-abrasive polishing beads and a solvent which is agitated to remove surface irregularities from the articles.
U.S. Pat. No. 5,571,558 discloses a tumbling process for removing flash from a molded IOL by applying a layer of aluminum oxide on a plurality of beads, placing the coated beads, alcohol, water and silicone IOLs in a container and tumbling the same to remove flash.
U.S. Pat. No. 5,725,811 discloses a process for removing flash from molded IOLs including tumbling the IOLs in a tumbling media of 0.5 mm diameter glass beads and 1.0 mm diameter glass beads, alcohol and water.
In recent years, IOLs have been purposely designed with sharp posterior edges which has been found to inhibit the migration of lens epithelial cells (LECs) between the IOL and posterior capsular bag, also known as posterior capsule opacification or “PCO” to those skilled in the art. One such method for creating a sharp posterior edge in an IOL is described in copending application Ser. No. 10/005,864 filed on Nov. 8, 2001 and of common ownership with the present application, the entire disclosure of which is incorporated herein by reference. Creating a sharp, discontinuous bend in the posterior capsule wall is widely recognized by those skilled in the art as an effective method for minimizing PCO. See, for example, Posterior Capsule Opacification by Nishi, Journal of Cataract & Refractive Surgery, Vol. 25, January 1999. This discontinuous bend in the posterior capsule wall can be created using an IOL having a posterior edge which forms a sharp edge with the peripheral wall of the IOL.
Thus, while polishing is a necessary step in the IOL manufacturing process to remove surface irregularities, a purposely formed, sharp, posterior edge is one area of the IOL which should not be polished. If this area of the IOL is not protected from the polishing operation, the sharp posterior edge will become rounded and not function to inhibit PCO as intended. There thus remains a need for a method for polishing only targeted areas of IOLs, especially IOLs having purposely formed sharp edges.